Patent 1 and Patent 2, which disclose technologies relevant to APD bias controllers, are described below.
Patent 1 (Chinese Patent Publication No.: CN1790946A) discloses an optical receiving module with overload protection for use in optical fiber communication. It comprises an avalanche photodiode, a DC/DC step-up circuit that provides a reverse bias voltage to the avalanche photodiode, and a sampling resistor for optical input detection; one end of the sampling resistor is connected to the output end of the DC/DC step-up circuit, a current-limiting protective resistor is serially connected between the other end of the sampling resistor and the pin of the reverse bias voltage of the avalanche photodiode, and the resistance of the current-limiting protective resistor is greater than the resistance of the sampling resistor.
In this patent, a serially connected resistor is used for the bias voltage, and the output voltage of the step-up circuit does not automatically adjust based on the level of the APD photocurrent; when the photocurrent approaches the overload point, the output power is relatively high, and most of the power is wasted on the current-limiting resistor. In multichannel APD applications, the waste of power is even greater.
Patent 2 (Chinese Patent Publication No.: CN201256288Y) discloses an avalanche photodiode bias device and circuit, wherein the device comprises a power supply unit, an avalanche photodiode, and a feedback component; the input end of the feedback component is connected to the output end of the power supply unit, the first output end of the feedback component is connected to the input end of the power supply unit; and the second output end of the feedback component is connected to the input end of the APD. Through the provision of bias overload to the avalanche photodiode, this utility model patent prevents the chip of the avalanche photodiode from burning out, improving the safety and repair cost of avalanche photodiode receivers.
In this patent, APD protection is provided through adjustment of the bias voltage by electrical current feedback; it has a small dynamic range and may not play a protective role. The response time through the DC/DC step-up circuit is usually 0.1 ms-10 ms; when the optical input power increases instantaneously in a time period shorter than the response time of the DC/DC step-up circuit, photocurrent overload and TIA bit errors will occur, and the APD/TIA may be damaged by the overload.